Accelerometers are devices that measure acceleration. Accelerometers may be used in vehicles as part of the collection of diagnostic data, the monitoring of performance of the vehicle, or as part of a control system of the vehicle.
Accelerometers may measure proper acceleration, which is the acceleration experienced by the accelerometer relative to freefall. An accelerometer may output the measured proper acceleration as three values, corresponding to the measured acceleration values along orthogonal axes of the accelerometer. When installing or placing an accelerometer in a vehicle, it can be important to be able to determine the relationship between the coordinate frame of the vehicle and the coordinate frame of the accelerometer. More particularly, in order to be able to take useful acceleration measurements, the coordinate frame of the accelerometer and the coordinate frame of the vehicle should be oriented with one another.
In high end installations, the physical accelerometer may be carefully placed and secured in a vehicle to guarantee orientation of the coordinate frame of the accelerometer and the coordinate frame of the vehicle. This type of installation of an accelerometer may not be possible or practical in all situations, such as with consumer grade vehicles (e.g., consumer automobiles).